Conventionally, there are two types of microscope configurations, upright and inverted. Generally, upright and inverted microscopes differ in the manner by which a specimen, an objective, and a light source are arranged with respect to each other. For example, in an upright microscope, the objective is arranged so that it is disposed vertically above the specimen and the light source is disposed vertically below the specimen. In an inverted microscope, the objective is arranged so that it is disposed vertically below the specimen and the objective is disposed vertically above the specimen. Accordingly, an optic train, that is the arrangement of lenses generally housed within a housing and used to reflect light from the light source and specimen to a user, is arranged either above or below the specimen along with the objective.
In both upright and inverted microscopes, focusing of the specimen is accomplished by way of a corresponding positioning of the specimen relative to the objective, specifically in such a way that a region of the specimen to be observed is arranged in a focal plane of the objective. In one example, the position of the specimen relative to the objective may be adjusted by moving the objective along an optical axis relative to the specimen. In this case, the specimen may be mounted on a conventional specimen slide or dish that is secured to a corresponding specimen holder on a microscope stage. In this example, the microscope stage may be fixed such that it does not move in the direction of the optical axis of the objective. In another example, the position of the specimen relative to the objective may be adjusted by mechanically moving the stage along the optical axis in order to focus on the desired specimen region. In this example, the position of the objective would be fixed along the direction of its optical axis. In both examples, the stage may also be configured so that it may horizontally move relative to a microscope body along a single plane in at least two directions, such as in an X and a Y direction.
In both examples, focusing of the specimen region is usually performed by the user by operating an interface element arranged on the microscope body, as a result of which either the objective or the microscope stage is positioned along the optical axis. The interface element may comprise a rotary knob. Rotation of the rotary knob by the user causes linear motion of the objective or the stage along the optical axis. Typically, the rotary knob is arranged proximal to a working surface on which the microscope rests.